Associations of Plasma Glutamatergic Metabolites with Alpha Desynchronization during Cognitive Interference and Working Memory Tasks in Asymptomatic Alzheimer's Disease.

Electroencephalogram (EEG) studies have suggested compensatory brain overactivation in cognitively healthy (CH) older adults with pathological beta-amyloid(Aß42)/tau ratios during working memory and interference processing. However, the association between glutamatergic metabolites and brain activation proxied by EEG signals has not been thoroughly investigated. We aim to determine the involvement of these metabolites in EEG signaling. We focused on CH older adults classified under (1) normal CSF Aß42/tau ratios (CH-NATs) and (2) pathological Aß42/tau ratios (CH-PATs). We measured plasma glutamine, glutamate, pyroglutamate, and γ-aminobutyric acid concentrations using tandem mass spectrometry and conducted a correlational analysis with alpha frequency event-related desynchronization (ERD). Under the N-back working memory paradigm, CH-NATs presented negative correlations (r = ~-0.74--0.96, p = 0.0001-0.0414) between pyroglutamate and alpha ERD but positive correlations (r = ~0.82-0.95, p = 0.0003-0.0119) between glutamine and alpha ERD. Under Stroop interference testing, CH-NATs generated negative correlations between glutamine and left temporal alpha ERD (r = -0.96, p = 0.037 and r = -0.97, p = 0.027). Our study demonstrated that glutamine and pyroglutamate levels were associated with EEG activity only in CH-NATs. These results suggest cognitively healthy adults with amyloid/tau pathology experience subtle metabolic dysfunction that may influence EEG signaling during cognitive challenge. A longitudinal follow-up study with a larger sample size is needed to validate these pilot studies.

Inhibitory control in WM gate-opening: Insights from alpha desynchronization and norepinephrine activity under atDCS stimulation.

Our everyday activities require the maintenance and continuous updating of information in working memory (WM). To control this dynamic, WM gating mechanisms have been suggested to be in place, but the neurophysiological mechanisms behind these processes are far from being understood. This is especially the case when it comes to the role of oscillatory neural activity. In the current study we combined EEG recordings, and anodal transcranial direct current stimulation (atDCS) and pupil diameter recordings to triangulate neurophysiology, functional neuroanatomy and neurobiology. The results revealed that atDCS, compared to sham stimulation, affected the WM gate opening mechanism, but not the WM gate closing mechanism. The altered behavioral performance was associated with specific changes in alpha band activities (reflected by alpha desynchronization), indicating a role for inhibitory control during WM gate opening. Functionally, the left superior and inferior parietal cortices, were associated with these processes. The findings are the first to show a causal relevance of alpha desynchronization processes in WM gating processes. Notably, pupil diameter recordings as an indirect index of the norepinephrine (NE) system activity revealed that individuals with stronger inhibitory control (as indexed through alpha desynchronization) showed less pupil dilation, suggesting they needed less NE activity to support WM gate opening. However, when atDCS was applied, this connection disappeared. The study suggests a close link between inhibitory controlled WM gating in parietal cortices, alpha band dynamics and the NE system.

Short-term transcutaneous vagus nerve stimulation increases pupil size but does not affect EEG alpha power: A replication of Sharon et al. (2021, Journal of Neuroscience).

BACKGROUND: Transcutaneous auricular vagus nerve stimulation (taVNS) has been tested as a potential treatment for pharmaco-resistant epilepsy and depression. Its clinical efficacy is thought to depend on taVNS-induced activation of the locus coeruleus and other neuromodulator systems. However, unlike for invasive VNS in rodents, there is little evidence for an effect of taVNS on noradrenergic activity. OBJECTIVE: We attempted to replicate recently published findings by Sharon et al. (2021), showing that short bursts of taVNS transiently increased pupil size and decreased EEG alpha power, two correlates of central noradrenergic activity. METHODS: Following the original study, we used a single-blind, sham-controlled, randomized cross-over design. Human volunteers (n = 29) received short-term (3.4 s) taVNS at the maximum level below the pain threshold, while we collected resting-state pupil-size and EEG data. To analyze the data, we used scripts provided by Sharon and colleagues. RESULTS: Consistent with Sharon et al. (2021), pupil dilation was significantly larger during taVNS than during sham stimulation (p = .009; Bayes factor supporting the difference = 7.45). However, we failed to replicate the effect of taVNS on EEG alpha power (p = .37); the data were four times more likely under the null hypothesis (BF10 = 0.28). CONCLUSION: Our findings support the effectiveness of short-term taVNS in inducing transient pupil dilation, a correlate of phasic noradrenergic activity. However, we failed to replicate the recent finding by Sharon et al. (2021) that taVNS attenuates EEG alpha activity. Overall, this study highlights the need for continued research on the neural mechanisms underlying taVNS efficacy and its potential as a treatment option for pharmaco-resistant conditions. It also highlights the need for direct replications of influential taVNS studies.

Exploring neural oscillations in numerical inductive reasoning: unveiling effects of top-down and bottom-up conflict.

Previous research has delved into the brain's response to top-down and bottom-up conflicts in numerical inductive reasoning. However, the specific neural oscillatory patterns associated with these conflict types in numerical inductive reasoning processing have remained elusive. In this study, we employed a number series completion task in which participants had to determine whether a given target number adhered to concealed rules. Three conditions were established: an identity condition (e.g., 13, 13, 13), a perceptual mismatch condition (representing bottom-up conflict, e.g., 13 13 ), and a rule violation condition (representing top-down conflict, e.g., 13 13 14). Our EEG results revealed significant distinctions: rule violation induced more pronounced alpha desynchronization compared to both perceptual mismatch and identity conditions. Conversely, perceptual mismatch was associated with increased theta synchronization in contrast to rule violation and the identity condition. These findings suggest that alpha desynchronization may indicate the integration of rules during top-down conflict, while theta synchronization may function as a mechanism to inhibit bottom-up perceptual interference in numerical inductive reasoning.

Is the Discount Really Favorable? The Effect of Numeracy on Price Magnitude Judgment: Evidence From Electroencephalography.

Attractive price promotion will induce an unreasonable willingness to purchase, especially through shopping. However, it is not clear how numeracy, one of the essential abilities for understanding and applying numbers, influences the process of purchase judgment. In total, 61 participants were recruited to perform a price promotion task using electroencephalography. The results showed that consumers with low numeracy performed worse than their peers with high numeracy at the behavioral level, and they also had lower P3b amplitude and less alpha desynchronization, regardless of price promotion frameworks. These findings provided evidence on the processing of price information and provided further insights into how numeracy impacts price magnitude judgment.

Behavioural and cerebral asymmetries of mirror movements are specific to rhythmic task and related to higher attentional and executive control.

Mirror movements (MM) refer to the involuntary movements or contractions occurring in homologous muscles contralateral to the unilateral voluntary movements. This behavioural manifestation increases in elderly. In right-handed adults, some studies report asymmetry in MM production, with greater MM in the right dominant hand during voluntary movements of the left non-dominant hand than the opposite. However, other studies report contradictory results, suggesting that MM asymmetry could depend on the characteristics of the task. The present study investigates the behavioural asymmetry of MM and its associated cerebral correlates during a rhythmic task and a non-rhythmic task using low-force contractions (i.e., 25 % MVC). We determined the quantity and the intensity of MM using electromyography (EMG) and cerebral correlates through electroencephalography (EEG) in right-handed healthy young and middle-aged adults during unimanual rhythmic vs. non-rhythmic tasks. Overall, results revealed (1) behavioural asymmetry of MM specific to the rhythmic task and irrespective of age, (2) cerebral asymmetry of motor activations specific to the rhythmic task and irrespective of age and (3) greater attentional and executive activations in the rhythmic task compared to the non-rhythmic task. In line with our hypotheses, behavioural and cerebral motor asymmetries of MM seem to be specific to the rhythmic task. Results are discussed in terms of cognitive-motor interactions: greater attentional and executive control required in the rhythmic tasks could contribute to the increased occurrence of involuntary movements in both young and middle-aged adults.

Electroencephalogram (EEG) Alpha Power as a Marker of Visuospatial Attention Orienting and Suppression in Normoxia and Hypoxia. An Exploratory Study.

While electroencephalogram (EEG) alpha desynchronization has been related to anticipatory orienting of visuospatial attention, an increase in alpha power has been associated to its inhibition. A separate line of findings indicated that alpha is affected by a deficient oxygenation of the brain or hypoxia, although leaving unclear whether the latter increases or decreases alpha synchronization. Here, we carried out an exploratory study on these issues by monitoring attention alerting, orienting, and control networks functionality by means of EEG recorded both in normoxia and hypoxia in college students engaged in four attentional cue-target conditions induced by a redesigned Attention Network Test. Alpha power was computed through Fast Fourier Transform. Regardless of brain oxygenation condition, alpha desynchronization was the highest during exogenous, uncued orienting of spatial attention, the lowest during alerting but spatially unpredictable, cued exogenous orienting of attention, and of intermediate level during validly cued endogenous orienting of attention, no matter the motor response workload demanded by the latter, especially over the left hemisphere. Hypoxia induced an increase in alpha power over the right-sided occipital and parietal scalp areas independent of attention cueing and conflict conditions. All in all, these findings prove that attention orienting is undergirded by alpha desynchronization and that alpha right-sided synchronization in hypoxia might sub-serve either the effort to sustain attention over time or an overall suppression of attention networks functionality.

Can cognitive behaviour therapy beneficially influence arousal mechanisms in psychosis?

Cognitive behavioural therapy for psychosis (CBTp) is an approved adjunct therapy for patients with psychotic disorders; however, we do not fully understand the neurobiological effects that this therapy may exert. Arousal, as measured by electroencephalography (EEG), provides a useful electrophysiological marker for assessing psychotic disorders. EEG studies may therefore serve as a useful measure for assessing the underlying effects of CBTp in psychotic disorders.

Theta- and alpha-band EEG activity in response to eye gaze cues in early infancy.

In order to elucidate the development of how infants use eye gaze as a referential cue, we investigated theta and alpha oscillations in response to object-directed and object-averted eye gaze in infants aged 2, 4, 5, and 9months. At 2months of age, no difference between conditions was found. In 4- and 9-month-olds, alpha-band activity desynchronized more in response to faces looking at objects compared to faces looking away from objects. Theta activity in 5-month-old infants differed between conditions with more theta synchronization for object-averted eye gaze. Whereas alpha desynchronization might reflect mechanisms of early social object learning, theta is proposed to imply activity in the executive attention network. The interplay between alpha and theta activity represents developmental changes in both kinds of processes during early infancy.

Action observation and motor imagery in performance of complex movements: evidence from EEG and kinematics analysis.

Motor imagery (MI) and action observation (AO) are considered effective cognitive tools for motor learning, but little work directly compared their cortical activation correlate in relation with subsequent performance. We compared AO and MI in promoting early learning of a complex four-limb, hand-foot coordination task, using electroencephalographic (EEG) and kinematic analysis. Thirty healthy subjects were randomly assigned into three groups to perform a training period in which AO watched a video of the task, MI had to imagine it, and Control (C) was involved in a distracting computation task. Subjects were then asked to actually perform the motor task with kinematic measurement of error time with respect to the correct motor performance. EEG was recorded during baseline, training and task execution, with task-related power (TRPow) calculation for sensorimotor (alpha and beta) rhythms reactive with respect to rest. During training, the AO group had a stronger alpha desynchronization than the MI and C over frontocentral and bilateral parietal areas. However, during task execution, AO group had greater beta synchronization over bilateral parietal regions than MI and C groups. This beta synchrony furthermore demonstrated the strongest association with kinematic errors, which was also significantly lower in AO than in MI. These data suggest that sensorimotor activation elicited by action observation enhanced motor learning according to motor performance, corresponding to a more efficient activation of cortical resources during task execution. Action observation may be more effective than motor imagery in promoting early learning of a new complex coordination task.

Visual symmetry in objects and gaps.

It is known that perceptual organization modulates the salience of visual symmetry. Reflectional symmetry is more quickly detected when it is a property of a single object than when it is formed by a gap between two objects. Translational symmetry shows the reverse effect, being more quickly detected when it is a gap between objects. We investigated the neural correlates of this interaction. Electroencephalographic data was recorded from 40 participants who were presented with reflected and translated contours in one- or two-object displays. Half of the participants discriminated regularity, half distinguished number of objects. An event-related potential known as the Sustained Posterior Negativity (SPN) distinguished between reflection and translation. A similar ERP distinguished between one and two object presentations, but these waves summed with the SPN, rather than altering it. All stimuli produced desynchronization of 8-13 Hz alpha oscillations over the bilateral parietal cortex. In the Discriminate Regularity group, this effect was right lateralized. The SPN and alpha desynchronization index different stages of visual symmetry discrimination. However, neither component displayed the Regularity × Objecthood interaction that is observed in speeded discrimination tasks, suggesting that integration of visual regularity with objectness is not inevitable. Instead, both attributes may be processed in parallel and independently.

An EEGLAB plugin to analyze individual EEG alpha rhythms using the "channel reactivity-based method".

A recent paper [1] proposed a new technique, termed the channel reactivity-based method (CRB), for characterizing EEG alpha rhythms using individual (IAFs) and channel (CAFs) alpha frequencies. These frequencies were obtained by identifying the frequencies at which the power of the alpha rhythms decreases. In the present study, we present a graphical interactive toolbox that can be plugged into the popular open source environment EEGLAB, making it easy to use CRB. In particular, we illustrate the major functionalities of the software and discuss the advantages of this toolbox for common EEG investigations. The CRB analysis plugin, along with extended documentation and the sample dataset utilized in this study, is freely available on the web at http://bio.dei.unipd.it/crb/.